Modulated pressure wave vapor generator

ABSTRACT

The current invention provides a modulated pressure wave vapor generator suitable for use outside of the laboratory. The vapor generator of the current invention produces a controlled analyte vapor sample without using bulk movement of gas. Additionally, the current invention compensates for changes in the environment to ensure discharge of the preferred volume of analyte from the vapor generator. Finally, the current invention provides a method for generating a controlled volume of analyte vapor suitable for calibrating vapor sensors.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/789,049, filed Apr. 23, 2007, now U.S. Pat. No. 7,757,539 whichclaims priority from U.S. Provisional Patent Application Ser. No.60/794,627 filed on Apr. 24, 2006, the entire contents of which areincorporated herein by reference.

STATEMENT AS TO FEDERALLY SPONSORED RESEARCH

This application was supported in part by a contract from the U.S. ArmyNight Vision and Electronic Sensors Directorate Contract#W909MY-04-C-0038. The United States Government may have rights in andto this application by virtue of this funding.

FIELD OF THE INVENTION

The current invention provides a vapor generator which utilizes amodulated pressure wave to generate a pre-determined amount of analytevapor. The vapor generator compensates for changes in temperatures bychanging the pressure wave used to generate the analyte sample.Additionally, the current invention provides a method of producing acontrolled portion of analyte vapor without the bulk movement of gas.

BACKGROUND OF THE INVENTION

Sensors and analyzers suitable for detecting trace amounts ofexplosives, narcotics and other vapors of interest require calibrationfrom time to time. Typically, these analytical devices are calibrated bymeasuring a controlled amount of the desired compound produced by avapor generator. Currently available vapor generators operate byinjecting a controlled amount of analyte into a stream of clean gas. Inpractice, the gas stream passes over a temperature controlled bed ofanalyte. The temperature of the bed is selected to continuously evolve acontrolled amount of analyte into the passing gas stream. Thus, thesesystems are capable of accurately producing gas streams containingminute amounts of nearly any analyte.

Unfortunately, currently available systems have several limitingcharacteristics which preclude their use in the field environment. Therequirement of a clean gas stream necessitates the use of a filtersystem or compressed bottled gas. Additionally, current vapor generatorsrely on precision pumps and flow meters to ensure an accurate andcontrolled gas flow rate. Finally, the operator must precisely controlthe analyte bed temperature to insure uniform evolution of the analyteinto the flowing gas. As a result of these limitations, currentlyavailable vapor generation systems are complex, bulky, power hungry andexpensive devices unsuitable for use in the field.

SUMMARY OF THE INVENTION

The current invention provides an apparatus for generating a controlledamount of analyte vapor while compensating for environmental changes.The apparatus of the current invention comprises a modulated pressurevapor generator having a source chamber for containing an analyte vapor.The source chamber preferably includes an orifice or pinhole opening forexpelling a controlled amount of analyte vapor into the environment.Cooperating with the source chamber is a pressure transducer capable ofgenerating an alternating air flow between the source chamber and theenvironment. Operation of the pressure transducer expels a controlledamount air saturated with analyte vapor through the pinhole opening intothe environment. The apparatus further includes at least oneenvironmental sensor, e.g. a temperature sensor, and a computerprogrammed to control the pressure transducer in response to readingsobtained by the sensor and inputs from an operator.

Additionally, the current invention provides a method for generating acontrolled amount of analyte vapor. In the method of the currentinvention, sufficient analyte is placed within a source chamber suchthat the air within the source chamber is saturated with analyte vapor.The source chamber is provided with or is in fluid communication with apressure transducer. Additionally, the source chamber preferably has anorifice or pinhole opening suitable for expelling the desired analytestream. As an initial step, the current invention provides for thecharacterization and standardization of the vapor generator. Thecharacterization of the vapor generator requires a determination of thephysical characteristics of the source chamber, measurement of theenvironmental conditions such as temperature and the determiningcharacteristics of the pressure wave generated by the pressuretransducer. In the method of the current invention, the temperature isdetermined by temperature sensors which cooperate with a suitablyprogrammed computer. Following temperature characterization, pressurewave characteristics such as frequency, duty cycle, amplitude, pulseshape and number of pulses in the pulse train are determined and storedwithin the computer. Following the characterization steps, a controlledamount of analyte vapor can be accurately produced from the sourcechamber by actuation of the pressure transducer. In this step, thepressure transducer is actuated forcing air saturated with analyte fromthe source chamber through the pinhole as a jet. The analyte saturatedair travels a short distance from the source chamber prior to stopping.Subsequently, the pressure transducer goes through an intake strokedrawing air near the pinhole back into the source chamber while leavingan analyte cloud in the environment. The final volume of analyte in theanalyte cloud is controlled by the pressure pulse generated by thepressure transducer. Therefore, the temperature sensor, the controllingcomputer and the pressure transducer cooperate to control the generationof the analyte cloud by varying the pressure pulse of the pressuretransducer. In this manner, the method of the current inventioncompensates for temperature variations by offering the pressure pulsesover a wide dynamic range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a sectional view of the vapor generator of the currentinvention.

FIG. 2 provides a representative view of the ejection of an analyte fromthe vapor generator of the current invention.

FIG. 3 provides a representative view of generation of an analyte cloud.

FIG. 4 is a sectional view of the vapor generator of the currentinvention fitted with an instrument interface.

FIG. 5 demonstrates sensor response under conditions of a fixed pulsetrain while varying the temperature.

FIG. 6 demonstrates sensor response when environmental conditions areheld constant and while varying the number of pulses in the pulse train.

FIG. 7 demonstrates sensor response when environmental conditions areheld constant and while varying the duty cycle of the pulse train.

DETAILED DISCLOSURE OF THE INVENTION

The current invention provides a pulsed pressure vapor generatorsuitable for use by workers in the field. For example, security guardswill find the current invention useful for calibrating vapor sensorsduring inspections of cargo and other goods. The pulsed pressure vaporgenerator of the current invention overcomes the deficiencies of theprior art devices by eliminating the temperature controlled analyte bedand removing the need for bulk movement of a carrier gas. In contrast toavailable vapor generators, the present invention compensates forenvironmental changes, including but not limited to temperature andpressure, during the generation of a controlled analyte cloud.

The vapor generator of the current invention produces an analyte vaporcloud suitable for calibrating sensors or sensing devices. Inparticular, the vapor generator of the current invention is useful forcalibrating sensors suitable for detecting explosives, narcotics,chemical warfare agents, biological warfare agents, industrial products,industrial byproducts, or their simulants. A non-limiting list ofanalytes useful within the vapor generator of the current inventionincludes TNT, RDX, DNT, amino-TNT, amino-DNT, PETN, nitrates, peroxides,musk ketone, musk xylene, nicotinamide, methyl salicylate, alcohols, andother aromatic and aliphatic hydrocarbon compounds.

With reference to the drawings, the current invention provides amodulated pressure wave vapor generator 10, referred to as vaporgenerator 10 herein. Vapor generator 10 comprises a source chamber 14 influid communication with a pressure transducer 18. A preferred pressuretransducer 18 is an electric speaker. In the preferred embodiment,source chamber 14 has a pin hole opening or orifice 22. Preferably,orifice 22 is sized to produce a jet of analyte-saturated gas duringoperation of pressure transducer 18. In the preferred embodiment, asealing device 23 such as a cap or plug is fitted into orifice 22 toprevent diffusion of analyte through orifice 22 during periods ofnon-use. Diffusion of analyte through orifice 22 may contaminate theexterior of vapor generator 10 leading to erroneous calibration of thesensor (not shown). Additionally, source chamber 14 is optionallyprovided with a fitting or other suitable valve or passageway (notshown) for supplying analyte to the interior of source chamber 14. Useof a fitting provides the ability to refresh the supply of analytewithin source chamber 14 during operations in the field without the needfor dismantling vapor generator 10.

Vapor generator 10 is controlled by a suitably programmed electronicdevice such as computer 30. Preferably, computer 30 controls theoperation of pressure transducer 18 in response to monitoredenvironmental conditions. Accordingly, vapor generator 10 is providedwith at least one environmental sensor 34 for monitoring environmentalconditions such as temperature. Environmental sensor 34 communicates themonitored condition to computer 30. In the preferred embodiment,pressure transducer 18 is provided with a power source 35. As depictedin FIG. 1, a standard AA battery is suitable for use in the currentinvention. Typically, power source 35 also provides power to computer 30and other components of vapor generator 10.

Finally, in the preferred embodiment, vapor generator 10 is providedwith an instrument interface 37. Instrument interface 37 may be threadedor press fit onto vapor generator 10. As shown in FIG. 1, instrumentinterface 37 includes a sensor port 39 and an analyte chamber 41. Asdepicted in FIG. 4, when instrument interface 37 is positioned on vaporgenerator 10, analyte chamber 41 and sensor port 39 are preferably influid communication with source chamber 14. However, since the primaryfunction of instrument interface 37 is to ensure consistent positioningof the sensor (not shown) to be calibrated relative to vapor generator10, flow of the analyte vapor through instrument interface 37 is not anecessity. Rather, instrument interface 37 may simply provide a stableconsistent mechanism for reproducibly positioning a sensor relative tovapor generator 10 for calibration.

In the preferred embodiment, port 39 is a positioning receptaclesuitable for receiving a sensor. Typically, a vapor sensor or similardevice is positioned against or within port 39 during calibration. Inthis manner, instrument interface 37 provides for accurate, reproduciblepositioning of the sensor. Additionally, instrument interface 37includes an analyte chamber 41. Analyte chamber 41 is defined wheninstrument interface 37 is pressed on or threaded on end 12 of vaporgenerator 10. In this arrangement, analyte chamber 41 receives theanalyte vapor cloud 43 produced by vapor generator 10. Thus, instrumentinterface 37 enhances the accuracy of the calibration of the sensor. Inthe embodiment depicted in FIG. 1, sealing device 23 is sized to fitsnuggly within port 39 and is placed within port 39 during periods ofnon-use. When instrument interface 37 is not used, tip 24 of sealingdevice 23 may be configured to fit within orifice 22.

The current invention further provides a method for generating acontrolled amount of analyte vapor suitable for calibrating a vaporsensor. The method of the current invention will be described withreference to the Figs.

According to the preferred method of the current invention, a sufficientquantity of analyte is placed in source chamber 14 prior to assembly ofpressure transducer 18 to source chamber 14. Alternatively, analyte issupplied to source chamber 14 through a fitting or valve (not shown). Asnoted above, resupply or replacement of analyte to source chamber 14 maybe through the fitting or by removal of pressure transducer 18. Theconcentration of analyte in source chamber 14 is sufficient to yield asaturated atmosphere of air and analyte vapor. The air utilized insource chamber 14 is atmospheric air provided by communication betweenthe interior of source chamber 14 and the exterior of source chamber 14through orifice 22. Thus, the method of the current invention does notrely upon stored gas or filtered air systems.

Prior to operation of vapor generator 10, the individual components mustbe characterized in order to ensure the accurate generation of ananalyte cloud. The characterization process provides computer 30 withthe data necessary to control vapor generator 10. Factors whichinfluence the amount of analyte generated by the vapor generator 10include its physical characteristics, such as the size and configurationof source chamber 14, the diameter and length of orifice 22 andcharacteristics of the pressure transducer used; environmental factorssuch as temperature; and characteristics of the pulse train such asfrequency, duty cycle, amplitude, pulse shape and number of pulses. Thephysical configuration of source chamber 14, orifice 22 and pressuretransducer 18 will preferably remain constant for each vapor generator10.

The environmental temperature is preferably monitored by environmentalsensor 34. During temperature characterization, the effect oftemperature differences on vapor generator 10 is determined by measuringthe vapor output in response to an unvarying pressure wave over a rangeof temperatures. Preferably, the temperature monitored is thetemperature of the source chamber as this temperature determines thevapor pressure of the analyte.

Additionally, pressure transducer 18 is characterized by individuallyvarying the pressure wave parameters while holding the remainingpressure wave components constant. During this step, the environmentalconditions are preferably maintained constant; however, compensationsfor changes in the environment can be made by computer 30 using thetemperature curves generated during temperature characterization. Whilethe characterization process has been described in the order oftemperature characterization followed by pressure wave characterization,one skilled in the art will recognize that pressure wave parameters maybe characterized first if the temperature is maintained as a constantduring such characterization.

During the temperature and pressure characterization steps, pressurepulses are generated within source chamber 14 by pressure transducer 18.The quantity of analyte ejected from source chamber 14 is measured by asuitable sensor for each characterization step. Accordingly, a series ofcontrolled pressure pulses are generated over a range of temperatures todetermine the quantity of analyte ejected from source chamber 14 foreach temperature. Similarly, a series of measurements are taken whilevarying components of the pressure pulse, either at a constanttemperature or with the sensor response corrected for temperature bycomputer 30 using the previously developed temperature curve. Theresulting data permits controlled generation of an analyte cloud inresponse to changes in temperature and desired analyte volume.

FIGS. 5-7 demonstrate the calibration of one embodiment of the currentinvention. In FIG. 5, the pressure pulse necessary to produce thedesired sample of analyte is determined over a range of temperatures.Further, in FIGS. 6 and 7 the change in percent quench demonstrates thesensor's response to changes in the pressure pulse. In FIG. 6, the dutycycle of the pressure pulse was varied while the temperature wasmaintained constant. In FIG. 7, the number of pulses in the pulse trainwas varied.

As represented by FIGS. 5-7, vapor output depends linearly on both theduty cycle and the number of pulses in the pressure wave. Thus, thecharacterization steps account for the parameters which directly impactthe performance of vapor generator 10. Specifically, thecharacterization steps determine the characteristics of the pressurepulse, the analyte's vapor pressure over a range of temperatures and thesource chamber's geometry. The ability of the current invention to varythe pressure pulse (or pulse train) over a wide dynamic range eliminatesthe need to control the temperature of source chamber 14 as the methodof the current invention corrects for temperature variations by alteringthe pressure pulses generated by pressure transducer 18.

Following characterization, an algorithm can be created to preciselycontrol analyte delivery into the environment. Methods for generatingalgorithms of this type are well known to those skilled in the art.Further, methods for programming computer 30 with such algorithms arealso well known in the art. In the preferred embodiment, a calibrationconstant is included in the algorithm to account for variations inmeasurement units.

Without intending to limit the scope of the current invention, thefollowing is one example of system characterization and the developmentof a control algorithm suitable for use in the method of the currentinvention. Those skilled in the art will recognize that other algorithmsmay be developed for the purposes of controlling vapor generator 10.

The characteristic equation of the vapor generator can be expressed as:M=ƒ(σ,χ,ε)where M is the analyte mass ejected from the generator, σ is a set ofconstant parameters describing the geometry of the vapor generator, χ isa set of controllable parameters governing the motion of the pressuretransducer, and ε is a set of uncontrolled environmental parameters.

To make analysis tractable, we assume that the function is separable:M=ƒ _(σ) ₁ (σ₁)·ƒ_(σ) ₂ (σ₂) . . . ƒ_(σ) _(m) (σ_(m))·ƒ_(χ) ₁ (χ₁)·ƒ_(χ)₂ (χ₂) . . . ƒ_(χ) _(n) (χ_(n))·ƒ_(ε) ₁ (ε₁)·ƒ_(ε) ₂ (ε₂) . . . ƒ_(ε)_(p) (ε_(p))Since the geometric parameters σ_(i) are constant, the equation reducestoM=C _(σ)·ƒ_(χ) ₁ (χ₁)·ƒ_(χ) ₂ (χ₂) . . . ƒ_(χ) _(n) (χ_(n))·ƒ_(ε) ₁(ε₁)·ƒ_(ε) ₂ (ε₂) . . . ƒ_(ε) _(p) (ε_(p))where C_(σ) is a constant.

To experimentally characterize the system, the first step is todetermine how the output magnitude depends on the environmentalvariables ε. To do this, each external variable must be externallycontrolled using a laboratory test jig. The output magnitude of thevapor generator can then be measured while varying one environmentalparameter at a time and keeping all control parameters constant.

The data from the above set of experiments provides the basis for the“environmental correction” portion of the algorithm by providing twoimportant kinds of information. Specifically, they identify theenvironmental parameters which significantly influence output magnitudeand the functional dependence of the output magnitude on thoseparameters.

The next step is to determine how the control parameters affect outputmagnitude. With the environmental parameters held constant by theexternal test jig, each control parameter can be varied one at a timeand the output magnitude measured. As with the environmental parameters,this data set provides the functional dependence of the output magnitudeon the important control parameters.

The final step in determining the system characteristic equation is tomeasure the constant C_(σ). This parameter is simply tuned such that,for a given combination of χ and ε, the output magnitude predicted bythe characteristic equation matches the measured value.

After completing the above steps, the algorithm is constructed. With thesystem equation known, the control problem reduces to finding a controlparameter χ_(o) such thatM _(d) =C _(σ)·ƒ(χ₀,ε₀)where M_(d) is the desired (user-selectable) output magnitude and ε_(o)gives the current environmental conditions. This equation likely hasmultiple solutions; the algorithm only needs to find one.

In developing an algorithm, it is useful to recognize that there are twotypes of control parameters. First are those parameters whose functionshave an upper bound. An example is the voltage applied to the pressuretransducer. Since this voltage is limited and the output magnitudeincreases monotonically with voltage, the function has an upper bound.Second are those parameters whose functions do not have an upper bound.An example of this type is the number of pulses. This distinctionimplies the following strategy:

-   -   1. Assume all parameters with upper bounds have the value of        their respective upper bounds.    -   2. Find a combination of parameters without upper bounds which        will generate an output magnitude slightly greater than desired.    -   3. Now vary the parameters with upper bounds to reduce the        output magnitude to the desired level.

It has been found that, for certain types of pressure transducers, theoutput magnitude can be adequately controlled by varying only the numberof pulses and the voltage applied to the transducer (i.e. the frequencyand duty cycle of the pulse train can be constant). If the onlyenvironmental variable considered is temperature, the characteristicequation is:M=C _(σ)·ƒ_(χ) ₁ (P)·ƒ_(χ) ₂ (V _(ƒ))·ƒ_(ε) ₁ (T).

Let ƒχ(χi) have the formƒ_(χ) ₁ (P)=a ₀ +a ₁ ·P+a ₂ ·P ²ƒ_(χ) ₂ (V _(ƒ))=b ₀ +b ₁ ·V _(ƒ) +b ₂ V _(ƒ) ²

These are second-order Taylor series. More terms could be used, butsolving for χ_(i) given ƒ_(χ) _(i) (χ_(i)) becomes more difficult.Furthermore, since V_(χ) is a fractional parameter, its equation isscaled such that ƒ_(χ) ₂ (1)=1. We let ƒ_(ε) ₁ (T) have the form

${f_{ɛ_{1}}(T)} = 10^{\alpha{({\frac{1}{T} - \frac{1}{T_{0}}})}}$where T is measured in Kelvin and T₀ is an arbitrary constant. Thisnon-intuitive form was chosen because it matches the vapor-pressureequation for the analyte in question (TNT).

Once the constants a_(i), b_(i), α, and C_(σ) have been determinedduring system characterization, a control algorithm can be implemented.In this example, the characteristic equation can be written as

${{f_{\chi^{1}}(P)} \cdot {f_{\chi^{2}}\left( V_{f} \right)}} = \frac{M}{C_{\sigma} \cdot {f_{ɛ1}(T)}}$For the moment, assume that V_(ƒ) is its maximum value of 1. Using thedesired output magnitude M_(d), the above equation reduces to

${{f_{\chi^{1}}(P)} = \frac{M_{d}}{C_{\sigma} \cdot {f_{ɛ\; 1}(T)}}},$which can be solved using the quadratic formula. The solution P_(c) tothis equation is then rounded up to the nearest whole number and used tofind V_(ƒ).

${f_{\chi^{2}}\left( V_{f} \right)} = \frac{M_{d}}{C_{\sigma} \cdot {f_{ɛ1}(T)} \cdot {f_{\chi^{1}}\left( P_{C} \right)}}$As before, this equation can be solved using the quadratic formula, andthe two control parameters have been found.

Utilization of vapor generator 10 subsequently entails the steps ofdetermining the desired amount of analyte to be generated, monitoringenvironmental conditions using environmental sensor 34, inputting theenvironmental data and analyte amount into computer 30 and controllingpressure transducer 18 by operation of computer 30 to generate thedesired amount of analyte vapor.

Thus, operation of vapor generator 10 is described schematically byFIGS. 2-3. Following the operator's inputting the amount of analyte tobe generated into computer 30 via user interface 32, the method of thepresent invention determines the temperature of source chamber 14 usingenvironmental sensor 34 and signals pressure transducer 18 to emit thenecessary pressure pulse as determined by computer 30. As demonstratedby FIG. 2, when initially actuated pressure transducer 18 goes throughan exhaust stroke generating a pressure pulse which forces air saturatedwith analyte out of source chamber 14 through orifice 22. Theanalyte-saturated air travels a short distance from source chamber 14prior to the intake stroke of pressure transducer 18. FIG. 3 depicts thecycling of pressure transducer 18 to an intake stroke which subsequentlydraws air near orifice 22 into source chamber 14 leaving a cloud 43 ofanalyte in the environment. Resulting analyte cloud 43 may be used tocalibrate vapor sensors. For example, explosives sensors may beadequately calibrated to detect trace amounts of explosives when theanalyte stored in source chamber 14 is TNT.

Preferably, when calibrating a sensor, an instrument interface 37,depicted in FIGS. 1 and 4 and described above, is used. Instrumentinterface 37 ensures that a sensing device is consistently calibrated byproviding a standard alignment between the sensing device and vaporgenerator 10. In the embodiment depicted in FIGS. 1 and 4, duringcalibration the sensor is positioned against or within port 39 ofinstrument interface 37 prior to generation of analyte cloud 43, therebyensuring a consistent relationship between vapor generator 10 and thesensor. Following generation of analyte cloud 43, the sensor iscalibrated to reflect the known quantity of analyte within the cloud. Ifinstrument interface 37 is used during the calibration process, analytecloud 43 is confined within analyte chamber 41 by vapor generator 10 andthe sensor positioned adjacent to or within port 39, thereby enhancingthe accuracy of the calibration of the sensor. While use of instrumentinterface 37 is preferred, satisfactory results can be achieved withoutuse of instrument interface 37.

Other embodiments of the current invention will be apparent to thoseskilled in the art from a consideration of this specification and/orpractice of the invention disclosed herein. Accordingly, the foregoingspecification is considered merely exemplary of the current invention.The true scope of the current invention is defined by the followingclaims.

1. A vapor generator comprising: a source chamber; a pressure transducerin fluid communication with the interior of said source chamber; anelectronic device suitable for controlling said pressure transducer; ananalyte located within said source chamber; and, wherein said pressuretransducer is capable of generating an alternating air flow between theinterior of said source chamber and the exterior environment such thatoperation of said pressure transducer displaces analyte from theinterior of said source chamber to the exterior environment.
 2. Thevapor generator of claim 1, wherein said source chamber has an orificeproviding fluid communication between the interior of said sourcechamber and the exterior of said source chamber.
 3. The vapor generatorof claim 2, wherein said orifice is a pin hole opening.
 4. The vaporgenerator of claim 1, further comprising a fitting carried by saidsource chamber, said fitting providing fluid communication between theexterior and interior of said source chamber and said fitting suitablefor supplying additional analyte to the interior of said source chamber.5. The vapor generator of claim 1, further comprising at least oneenvironmental sensor.
 6. The vapor generator of claim 5, wherein saidenvironmental sensor is a temperature sensor positioned to monitor thetemperature of said source chamber.
 7. The vapor generator of claim 1,wherein said source chamber contains an atmosphere saturated withanalyte vapor.
 8. A vapor generator comprising: a source chamber, saidsource chamber has an orifice providing fluid communication between theinterior of said source chamber and the exterior of said source chamber;a pressure transducer in fluid communication with the interior of saidsource chamber, said pressure transducer capable of generating analternating air flow between the interior of said source chamber and theexterior of said source chamber; an electronic device suitable forcontrolling said pressure transducer; atmospheric air located withinsaid source chamber, said atmospheric air saturated with an analytevapor; at least one environmental sensor; and, wherein operation of saidpressure transducer displaces analyte vapor from the interior of saidsource chamber to the exterior of said source chamber.
 9. The vaporgenerator of claim 8, wherein said orifice is a pin hole.
 10. The vaporgenerator of claim 8, further comprising a fitting carried by saidsource chamber, said fitting providing fluid communication between theexterior and interior of said source chamber and said fitting suitablefor supplying additional analyte to the interior of said source chamber.11. The vapor generator of claim 8, wherein said environmental sensor isa temperature sensor positioned to monitor the temperature of saidsource chamber.
 12. A vapor generator comprising: a source chamber, saidsource chamber has an orifice providing fluid communication between theinterior of said source chamber and the exterior of said source chamber,wherein said source chamber contains atmospheric air; a pressuretransducer in fluid communication with the interior of said sourcechamber, said pressure transducer capable of generating an alternatingair flow between the interior of said source chamber and the exterior ofsaid source chamber; atmospheric air located within said source chamber,said atmospheric air saturated with analyte vapor; at least oneenvironmental sensor, said sensor positioned to monitor theenvironmental conditions of said source chamber; an electronic deviceprogrammed to control said pressure transducer in response to readingsobtained by the sensor, whereby said operation of said pressuretransducer in response to said electronic device displaces analyte vaporfrom the interior of said source chamber through said orifice to theexterior of said source chamber.
 13. The vapor generator of claim 12,wherein said orifice is a pin hole opening.
 14. A method for generatinga controlled amount of vapor comprising: placing a vapor producingmaterial in a source chamber, wherein the interior of said sourcechamber is in fluid communication with the exterior environment andwherein the atmosphere within said source chamber comprises atmosphericair; saturating the air within said source chamber with the vapor fromsaid vapor producing material; monitoring environmental conditionswithin said source chamber; and, passing a pressure wave through saidsource chamber thereby producing a vapor cloud to the exterior of saidsource chamber wherein said pressure wave is controlled in response tomonitored environmental conditions.
 15. The method of claim 14, furthercomprising the step of positioning a temperature sensor within saidsource chamber and using said temperature sensor to carryout said stepof monitoring environmental conditions and wherein said method furthercomprises the step of varying the temperature of said source chamberwhile generating said vapor cloud thereby determining the effect ofchanges in temperature on the generation of said vapor cloud.
 16. Themethod of claim 14, further comprising the step of assembling a pressuretransducer to said source chamber after placing said vapor producingmaterial in said source chamber.
 17. The method of claim 14 furthercomprising the step generating a jet of analyte saturated air by passingsaid vapor through an orifice, said orifice providing fluidcommunication between the interior and exterior of said source chamber,thereby producing said vapor cloud.
 18. The method of claim 14, whereinsaid pressure wave generates a controlled amount of analyte vapor to theexterior of said source chamber.